Re: [Xen-devel] [PATCH v4 4/7] xen/x86: use invpcid for flushing the TLB

[Juergen Gross <jgross@xxxxxxxx>]

On 29/03/18 15:44, Jan Beulich wrote:
>>>> On 27.03.18 at 11:07, <jgross@xxxxxxxx> wrote:
>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -63,6 +63,10 @@ boolean_param("nosmp", opt_nosmp);
>>  static unsigned int __initdata max_cpus;
>>  integer_param("maxcpus", max_cpus);
>>  
>> +/* opt_invpcid: If false, don't use INVPCID instruction even if available. 
>> */
>> +static bool __initdata opt_invpcid = true;
>> +boolean_param("invpcid", opt_invpcid);
> 
> Hmm, I'm sorry for noticing only now (while seeing the questionable
> uses of cpu_has_invpcid in patch 7), but this being an init-only
> variable and having ...
> 
>> @@ -1549,6 +1553,9 @@ void __init noreturn __start_xen(unsigned long mbi_p)
>>      if ( cpu_has_fsgsbase )
>>          set_in_cr4(X86_CR4_FSGSBASE);
>>  
>> +    if ( !opt_invpcid )
>> +        setup_clear_cpu_cap(X86_FEATURE_INVPCID);
> 
> ... this effect has two issues: For one, in such a case this should
> be a sub-option to "cpuid=". And then afaict it also disables use of
> INVPCID in HVM guests. IOW I think you want to retain the option
> but make the variable non-init and non-static. Obviously for early
> boot use it may then no longer be possible to set it to true at build
> time (you may end up needing two variables).

Okay. I'll change it.


Juergen

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